Why cant we have like a point system,Threads started,Polls,Posts stuff like that and then when you reach a certain point levle you get a special privlidge,E.g 100 points Custom AV ,200 points Custom sig,etc etc.Or you could have an auction with those points,Like a currency for the thread.

Just an idea

EDIT;I just thought of another idea,A Personal Blog for every user

The flaw with this is that on forums, quality is preferred over quantity, it'd be weird to rate how many points you got for what too. Point system is basically what our rep system is, which is also not very accurate in guaging people's performance on the forum since not everyone bothers to rep.
Your idea has a good concept, it'd just get abused though.